1. Field of the Invention
The present invention relates to technologies adopted in conjunction with a battery module that includes a plurality of cells and more specifically, it relates to a technology for improving the battery cell cooling performance, a technology for improving the level of venting performance with regard to gas generated by the battery cells.
2. Description of Related Art
A safety valve is disposed in a battery cell such as a lithium ion battery used in a hybrid electric car, a pure electric car or the like. The safety valve is designed to open as an abnormal condition such as internal short-cut or an overcharge causes an increase in the internal pressure at the battery. As the safety valve opens, the electrical connection between the terminal and the electrode is cut off and a gas (e.g., a carbon oxide gas) is discharged from the battery. While the gas is harmless, it is not desirable that it be released into the cabin of the vehicle and is, therefore, released into a passage or a chamber that is separate from a cooling medium passage through which the medium used to cool the battery cell is distributed, so as to ensure that the gas will not be released within the vehicle. The gas is then led outside the vehicle via a piping or the like. Japanese Laid Open Patent Publication No. 2004-14421 (patent reference 1) discloses a battery module adopting such a separation structure.
In the battery module disclosed in patent reference 1, three spaces, i.e., a first space through which a cell cooling medium flows, a second space into which the gas discharged from the cells is released and a third space where a connecting plate that electrically connects a plurality of cells is installed, are formed in sequence inside the battery module case. Thus, since the ends of the cells, ranging through the second space, are present in the third space, the cooling medium flowing through the first space contacts the cells over a small contact area, i.e., a small cooling area, in the battery module disclosed in patent reference 1.
In addition, a pipe through which the gas released into the second space is guided to the outside of the battery module is disposed over an upper area of the battery module disclosed in patent reference 1. However, the gas is emitted from the cells as a vapor containing the electrolyte. Thus, while the gas emitted from the cells can be expelled through the pipe, any liquid such as the electrolyte in the gas cannot be expelled and instead is collected at the bottom of the second space in the battery module disclosed in patent reference 1.